The objective of this program is to develop a standardized procedure for the preparation of technetium orthophosphate for bone imaging. The orthophosphate is chosen because of its low toxicity, its stable chemical form and its availability. To assure a reproducible product an exhaustive analytical program involving liquid chromatography, spectroscopy and potentiometric titrations will be undertaken to determine the critical variables involved in the preparation. In addition the chemical species present in vitro and in vivo will be determined in order to shed light on the mechanism of metal uptake in bone and give a basis for complete quality assurance of the product. The immediate use of this development will be in the W.H.C. Department of Nuclear Medicine and in the affiliated community radiopharmacy service.